From 0ab548cb905318645ef680a0ea93efdf3d89e2df Mon Sep 17 00:00:00 2001
From: larabr <7375870+larabr@users.noreply.github.com>
Date: Tue, 2 Sep 2025 14:20:59 +0200
Subject: [PATCH] Fix zlib compression for data larger than 65KB

Regression introduced in https://github.com/openpgpjs/openpgpjs/pull/1826
(v6.2.0) .
Due to internal fflate lib changes, part of the compressed data ended up being discarded,
leading to a corrupted compressed payload for the encrypted/signed message,
which cannot be decompressed.

Compression is disabled by default in openpgpjs.
Hence, the issue affects only users who enabled zlib compression via e.g.
`config.preferredCompressionAlgorithm = openpgp.enums.compression.zlib`
and encrypted or signed data larger than 65KB.
---
 src/packet/compressed_data.js |  8 ++++++--
 test/general/openpgp.js       | 20 ++++++++++++++++++++
 2 files changed, 26 insertions(+), 2 deletions(-)

diff --git a/src/packet/compressed_data.js b/src/packet/compressed_data.js
index cdeddea0..fa7fddc2 100644
--- a/src/packet/compressed_data.js
+++ b/src/packet/compressed_data.js
@@ -151,8 +151,12 @@ function zlib(compressionStreamInstantiator, ZlibStreamedConstructor) {
       return streamFromAsync(() => streamReadToEnd(data).then(inputData => {
         return new Promise((resolve, reject) => {
           const zlibStream = new ZlibStreamedConstructor();
-          zlibStream.ondata = processedData => {
-            resolve(processedData);
+          const processedChunks = [];
+          zlibStream.ondata = (processedData, final) => {
+            processedChunks.push(processedData);
+            if (final) {
+              resolve(util.concatUint8Array(processedChunks));
+            }
           };
           try {
             zlibStream.push(inputData, true); // only one chunk to push
diff --git a/test/general/openpgp.js b/test/general/openpgp.js
index 4558cb5c..d626522b 100644
--- a/test/general/openpgp.js
+++ b/test/general/openpgp.js
@@ -3698,6 +3698,26 @@ XfA3pqV4mTzF
             });
           });
 
+          it('should encrypt and decrypt with one password (larger message)', async function () {
+            const largerPlaintext = new Uint8Array(100_000);
+            const encOpt = modifyCompressionEncryptOptions({
+              message: await openpgp.createMessage({ binary: largerPlaintext }),
+              passwords: password1
+            });
+            const decOpt = {
+              passwords: password1,
+              format: 'binary'
+            };
+            return openpgp.encrypt(encOpt).then(async function (encrypted) {
+              decOpt.message = await openpgp.readMessage({ armoredMessage: encrypted });
+              return openpgp.decrypt(decOpt);
+            }).then(function (decrypted) {
+              expect(util.equalsUint8Array(decrypted.data, largerPlaintext)).to.be.true;
+              expect(decrypted.signatures.length).to.equal(0);
+              verifyCompressionDecrypted(decrypted);
+            });
+          });
+
           it('Streaming encrypt and decrypt small message roundtrip', async function() {
             const plaintext = [];
             let i = 0;